Electrocoagulation-Electroflotation for Primary Treatment of Animal Rendering Wastewater to Enable Recovery of Fats

Abstract

Rendering wastewater (RW) contains high levels of fats collected from material processed during rendering. Primary treatment of RW to remove floatable fats is necessary for to avoid issues in downstream treatment. Recovery of waste fats that can be sent back to the rendering process can be of value to the rendering enterprise. Dissolved air flotation (DAF) is commonly used for primary treatment of RW but requires polymer coagulants that must be minimized to keep their concentrations low in the recovered fat stream. Oxidation of fats caused by dissolved air is another undesirable effect of DAF. In this work, RW was treated by electrocoagulation-electroflotation (EC-EF) in a novel horizontally-placed electrode pair design as an alternative to DAF. EC-EF performed better in COD removal with increasing current densities. In situ flotation within the electrochemical cell was able to concentrate and preserve long chain fatty acids (LCFA). Treatment at higher current densities within the electrochemical cell generated surplus cation release and allowed further coagulation in a subsequent step. Longer mixing duration in the post-electrochemical treatment step resulted in increased overall COD removal. The overall COD removal for EC-EF with applied current densities of 2 mA/cm2 reached 69.49 ± 4.83% after 15 minutes of mixing at 100 rpm followed by 15 minutes of sedimentation. EC-EF thus not only provides competitive treatment performance for RW, but also recovery of well-preserved rendering products.